1. Field of the Invention
The invention relates to a wiring board in which a wiring pattern is formed on a substrate and a gas discharge type display apparatus using such a wiring board.
2. Description of the Related Art
According to a gas discharge type display apparatus such as a plasma display or the like, since a display is performed by a self light emission, an angle of visibility is wide and a display can be easily seen. Such a display apparatus has features that a thin display apparatus can be manufactured and a large screen can be realized and the like. An application of such a display apparatus to a display apparatus of information terminal equipment or a high definition television receiver has been started. The plasma display is mainly classified into a DC driving type and an AC driving type. According to the plasma display of the AC driving type among them, a luminance is high owing to a memory function of a dielectric layer covering electrodes and a life enough to endure an actual use can be obtained due to the formation of a protecting layer or the like. Thus, the plasma display has been put into practical use as a multi-purpose video monitor.
FIG. 6 is a perspective view showing a structure of a plasma display panel which has been put into practical use. To make it easy to see, a front substrate 100 is illustrated in the diagram so as to be away from a back substrate 200 and a discharge space area 300.
The front substrate 100 has a structure such that display electrodes 600 made of a transparent electrode material such as ITO (Indium Tin Oxide), tin oxide (SnO2), or the like, bus electrodes 700 made of a low resistance material, a dielectric layer 800 made of a transparent insulating material, and a protecting layer 900 made of a material such as magnesium oxide (MgO) or the like are formed on a front glass substrate 400.
The back substrate 200 has a structure such that address electrodes 1000, barrier ribs 1100, and a fluorescent layer 1200 are formed on a back glass substrate 500. Although not shown, a dielectric layer is also formed on the address electrodes 1000.
By adhering the front substrate 100 and back substrate 200 so that the display electrodes 600 and address electrodes 1000 almost perpendicularly cross, the discharge space area 300 is formed between the front substrate 100 and back substrate 200.
In the gas discharge type display apparatus, an AC voltage is applied between a pair of display electrodes 600 formed on the front substrate 100 and a voltage is applied between the address electrodes 1000 formed on the back substrate 200 and the display electrodes 600, thereby generating an address discharge and allowing predetermined discharge cells to generate a main discharge. By ultraviolet rays which are generated by the main discharge, the fluorescent materials 1200 of red, green, and blue separately coated on the discharge cells are allowed to emit light, thereby displaying.
A conventional technique of such a gas discharge type display apparatus has been disclosed in, for example, xe2x80x9cFlat Panel Display 1996xe2x80x9d, edited by Nikkei Microdevice, pages 208-215, 1995.
A method of forming the bus electrodes 700 provided for the front substrate 100 and the address electrodes 1000 provided for the back substrate 200 will be described further in detail. FIGS. 4 and 5 show an example of forming the address electrode 1000 onto the back glass substrate 500. Since the bus electrodes 700 provided for the front substrate 100 are also formed by almost similar steps, its description is omitted here.
First referring now to FIG. 4, Cr/Cu/Cr layers (1000a to 1000c) serving as an address electrode 1000 and a resist 2500 to form a pattern of the address electrode 1000 are sequentially formed on the back glass substrate 500 so as to be laminated by using a film forming method such as sputtering method, evaporation deposition method, or the like and by using a resist forming method such as rotational coating, laminating, or the like (step (a): film forming step). Subsequently, the resist 2500 is exposed and developed so as to obtain a desired pattern of the address electrode 1000 (steps (b) and (c): photolithographic step). The Cr layer 1000a is etched in a desired pattern by using an etchant for Cr (step (d): etching step). Subsequently, the exposed and developed resist 2500 is removed and the resist 2500 is again formed (steps (e) and (f)). Subsequently, referring to FIG. 5, by repeating the above processes with respect to each of the Cu layer 1000b and Cr layer 1000c (steps (g) to (o)), the address electrode 1000 is formed on the back glass substrate 500.
Although such a process is usually called a photolithograph-etching process, such a process has difficulties that the number of steps is large and costs are high because the resist formation and the like are included. Although the forming method of the Cr/Cu/Cr wirings has been described here, there are similar difficulties so long as a resist is used even if wirings are formed by using another single material. Although a mask to expose and form the resist pattern is necessary to form a resist, according to the gas discharge type display apparatus, since it ordinarily has a large screen, a positional deviation occurs more easily as a position of the mask approaches a periphery and it is difficult to accurately form wirings. It is also difficult to realize a highly accurate position matching itself of the mask. The mask is expensive.
As a wiring forming method in which the resist is made unnecessary, there is a method whereby a photosensitive material (for example, silver material having photosensitivity) is used and the photosensitive material is exposed and developed by a light source such as a mercury lamp or the like, thereby forming wirings.
In this case as well, however, in case of exposing the photosensitive material, a mask on which a desired wiring pattern has been formed is necessary and the difficulties in case of using the mask as mentioned above still remain. That is, there are the difficulties of the positional deviation at the time of formation of the wirings, the positional mismatching of the mask, and the costs of the mask.
It is an object of the invention to provide an exactly novel process which makes a mask unnecessary. That is, an object of the invention is to provide a gas discharge type display apparatus in which wirings are formed by exactly novel processes without needing a mask.
According to the invention, when wirings are formed by using a photosensitive material, a wiring pattern is directly drawn by a laser and the photosensitive material is exposed by the laser drawing, thereby making the conventional mask unnecessary. That is, according to the invention, to accomplish the above object, a front substrate having a plurality of first electrodes and a back substrate having a plurality of second electrodes are provided, and at least ones of the first and second electrodes are made of a photosensitive material containing silver exposed by using the laser.
As mentioned above, by directly drawing and exposing the photosensitive material with the laser, the conventional exposing process using the mask is unnecessary, so that the difficulties of the positional deviation at the time of the formation of the wirings due to the mask, the positional mismatching of the mask, and the costs of the mask can be solved. Therefore, according to the gas discharge type display apparatus of the invention, there is no positional mismatching of the mask and high positioning precision of the wirings can be easily assured, namely, the wirings can be formed at a desired position as compared with the conventional apparatus, so that uniform discharging characteristics can be obtained on the whole panel surface.
The wirings can be also formed at low costs.
Silver is preferable as a photosensitive material because of a wiring resistance or the like.